What is the optimal thickness range of aluminum foil for infant formula cans of different specifications?

1. Увод: Core Value of Aluminum Foil Thickness for Infant Milk Powder Cans

Thickness of aluminum foil for infant formula cans, characterized by high protein and lactose content, has strict requirements for storage conditions: oxygen causes whey protein oxidation (deterioration occurs when carbonyl compound content exceeds 0.8mg/g), moisture migration leads to caking (failure when moisture content >5%), and light accelerates the degradation of vitamins A/D (30% loss rate after 12 hours of light exposure). As the core barrier layer for can mouth sealing, the thickness of алуминијумска фолија directly determines three key indicators:

1. Barrier Effectiveness: Controlling Oxygen Transmission Rate (ОТР) ≤0.1 cm³/(m²・24h・0.1MPa) and Water Vapor Transmission Rate (ВВТР) ≤0.1 g/(m²・24h);

2. Mechanical Adaptability: Adapting to forming processes of different can types (circular stamping, square edge folding) to avoid cracking or seal failure;

3. Safety Compliance: Meeting heavy metal migration requirements for food-contact materials (lead/cadmium ≤0.01mg/kg).

The structural differences between circular cans (symmetrical stress) and square cans (stress concentration at corners) necessitate tailored aluminum foil thickness designs, which have long been a key technical focus in the industry.

2. Correlation Between Mainstream Specifications of Infant Milk Powder Cans and Aluminum Foil Thickness

(1) Basic Parameters: Can Type Specifications and Functional Positioning of Aluminum Foil

Current mainstream capacities of infant milk powder cans are divided into three categories: 180-200г (portable), 400-500г (medium-capacity), and 800-1200g (large-capacity), with corresponding can mouth diameters/side lengths and aluminum foil coverage areas as follows:

Aluminum foil must simultaneously serve as a “преградни слој” и “sealing carrier”. Excessively thin foil (<0.02мм) is prone to pinholes (≥2 pinholes per m² renders it invalid), while excessively thick foil (>0.05мм) causes forming cracks (especially high risk at square can corners). Thus, differentiated thickness ranges are required for different can types.

(2) Circular Cans: Thickness Optimization for Symmetrical Structure (0.025-0.04мм)

1. Basis for Thickness Range Determination

The mouth of a circular can is symmetrically round, so aluminum foil bears uniform stress during stamping forming, with no obvious stress concentration areas. Стога, a relatively wide thickness range is applicable:

• 180-200g Small-Capacity Cans: 0.025-0.03mm aluminum foil (Нпр., 8011-O temper) is selected. Test results show OTR ≤0.08 cm³/(m²・24h・0.1MPa) and WVTR ≤0.07 g/(m²・24h), meeting the 6-month shelf-life requirement. У међувремену, the foil has moderate stiffness (stiffness value ≥0.5 mN・m), suitable for manual opening.

• 400-500g Medium-Capacity Cans: 0.03-0.035mm aluminum foil is used, combined with a 20μm PE heat-sealing layer. The heat-sealing strength reaches 12 N/15mm, which can withstand internal negative pressure (-0.02МПа) without delamination. The seal qualification rate of this specification product from Chinalco Group reaches 99.8%.

• 800-1200g Large-Capacity Cans: Thickness needs to be increased to 0.035-0.04mm to enhance puncture resistance (puncture strength ≥4.2 N), preventing foil damage caused by repeated spoon access. Tests by Mingtai Aluminum show that the damage rate of this thickness foil in 1200g cans is only 0.05%.

2. Key Performance Verification

Laboratory comparison tests indicate: When the aluminum foil thickness for circular cans is less than 0.025mm, the pinhole rate increases from 0.1% да 1.2%, and the average OTR rises from 0.08 да 0.23 cm³/(m²・24h・0.1MPa), failing to meet the 12-month shelf-life requirement for cans over 800g. When thickness exceeds 0.04mm, the stamping qualification rate drops from 99.5% да 97.3%, and the opening force increases from 6-8 N to 10-12 N, which does not comply with the “easy opening” standard for infant products (ГБ / Т 35871-2020 requires opening force ≤9 N).

(3) Square Cans: Precise Thickness Control for Angled Structure (0.022-0.035мм)

1. Basis for Thickness Range Determination

The mouth of a square can has 4 right-angle (90°) углови. During forming, the aluminum foil at the corners has an elongation rate of 15-20% (only 5-8% for circular cans), making it prone to cracking or wrinkling due to improper thickness. Thus, more precise thickness control is required:

• 180-200g Small-Capacity Cans: 0.022-0.028mm aluminum foil (Нпр., 3003-H18 temper) is selected, with an elongation rate of 18-20% that adapts to the stretching demand at corners. The measured damage rate at corners is <0.1%. У међувремену, WVTR stabilizes at 0.06-0.08 g/(m²・24h), meeting the short-term (3-6 месецима) storage requirement for portable cans.

• 400-500g Medium-Capacity Cans: 0.028-0.032mm aluminum foil is used, combined with the “pre-folding process” (folding the foil at corners into 45° in advance) to reduce forming stress. This increases the heat-sealing qualification rate from 98.2% да 99.6%, with an average OTR ≤0.07 cm³/(m²・24h・0.1MPa).

• 800-1200g Large-Capacity Cans: Thickness must be controlled at 0.032-0.035mm, и “gradient-thickness aluminum foil” (thickness at corners is 0.002-0.003mm thinner than that of the flat area) is required. This ensures puncture resistance (≥4.0 N) in the flat area while avoiding corner cracking. After adopting this solution for square cans, Feihe Dairy extended the shelf life to 18 месецима.

2. Structural Adaptability Verification

When the aluminum foil thickness for square cans exceeds 0.035mm, the tensile stress at corners surges from 25MPa to 40MPa, and the cracking rate increases from 0.2% да 3.5%. When thickness is less than 0.022mm, the flat area is prone to depression due to can mouth pressure (≥0.05MPa), leading to seal failure. The measured poor seal rate reaches 2.8%, much higher than 0.5% for circular cans.

3. Core Factors Influencing Aluminum Foil Thickness Selection

(1) Quantitative Correlation Between Barrier Performance and Thickness

Према Aluminum and Aluminum-Plastic Composite Films for Food Packaging (T/CNPPA 3003-2022), aluminum foil thickness is positively correlated with barrier performance, but the growth rate slows down beyond the critical value:

• Баријера кисеоника: When thickness increases from 0.02mm to 0.03mm, OTR decreases from 0.15 да 0.07 cm³/(m²・24h・0.1MPa) (53% reduction); when thickness increases from 0.03mm to 0.04mm, OTR only decreases from 0.07 да 0.05 cm³/(m²・24h・0.1MPa) (28% reduction).

• Препрека влаге: At 0.025mm thickness, WVTR is 0.09 g/(m²・24h); at 0.03mm, it drops to 0.06 g/(m²・24h); when thickness further increases to 0.04mm, WVTR only decreases to 0.05 g/(m²・24h), showing a significant decline in marginal benefits.

Стога, the thickness of aluminum foil for infant milk powder cans does not need to be unnecessarily increased; уместо тога, а “barrier-cost” balance should be found based on can structure.

(2) Mechanical Performance and Forming Process Requirements

1. Tensile Strength and Crack Resistance

The aluminum foil at square can corners requires an elongation rate ≥18%. For 8011-O temper aluminum foil in the 0.022-0.035mm thickness range, the elongation rate stably remains at 18-22%, meeting the requirement. When thickness exceeds 0.035mm, the elongation rate drops below 15%, making it prone to cracking.

2. Heat-Sealing Adaptability

Aluminum foil needs to be compounded with a PE heat-sealing layer. Excessively thick foil (>0.04мм) increases the heat-sealing temperature (from 120℃ to 140℃), easily aging the PE layer; excessively thin foil (<0.02мм) results in insufficient heat-sealing strength (<8 N/15mm), failing to meet GB/T 28118-2011 захтеви (≥10 N/15mm).

3. Отпорност на пробијање

Large-capacity cans (>800г) need to withstand spoon puncture. When aluminum foil thickness is ≥0.035mm, the puncture strength is ≥4.0 N, preventing leakage after puncture. For small-capacity cans with low access frequency, 0.025дебљина мм мм (puncture strength ≥3.0 N) is sufficient.

(3) Compliance and Safety Standards

Infant food packaging must meet stricter safety requirements:

• Heavy Metal Migration: According to GB 4806.9-2023, the lead and cadmium migration of aluminum foil must be ≤0.01mg/kg. Excessively thin foil (<0.02мм) is prone to impurity introduction during production, increasing migration risks; when thickness >0.05мм, aluminum migration may exceed the limit (test results show 0.12mg/kg aluminum migration for 0.05mm foil, close to the 0.15mg/kg limit).

• Microbial Control: Aluminum foil must undergo 121℃/30min sterilization. The 0.022-0.04mm thickness range ensures sterilization uniformity (temperature deviation ≤2℃); excessively thick foil leads to incomplete sterilization, while excessively thin foil is easily damaged by high temperatures.

4. Industry Standards and Thickness Quality Control System

(1) Key Standard Framework

(2) Full-Process Thickness Quality Control

1. Substrate Testing: A laser thickness gauge (accuracy ±0.1μm) is used, with sampling every 10m to ensure thickness deviation within ±5%;

2. Forming Testing: After stamping aluminum foil for circular cans, an optical microscope is used to check pinholes (≤1 pinhole/m²); after folding square cans, the tensile strength at corners is tested (≥15MPa);

3. Finished Product Testing: After sealing, a thermal shock test (-20℃~40℃ cycle 5 times) is conducted, requiring no leakage and a barrier performance retention rate ≥90%.

5. Thickness Optimization Paths and Future Trends

(1) Customized Thickness Design

1. Precise Matching by Can Type and Capacity

• • 180-200g circular cans: 0.025-0.03мм (balancing lightweight and barrier performance);

• • 800-1200g square cans: 0.032-0.035мм (gradient thickness to prevent corner cracking);

2. Adjustment Based on Storage Conditions

In tropical regions (RH≥85%), thickness needs to be increased by 0.002-0.003mm to achieve WVTR ≤0.06 g/(m²・24h); for cold chain storage, the lower limit thickness can be maintained to reduce costs.

(2) Material and Process Innovation

1. Nanocoating Modification: Coating a 50-100nm SiO₂ nanocoating on the surface of 0.022mm aluminum foil reduces OTR from 0.15 да 0.08 cm³/(m²・24h・0.1MPa), which can replace traditional 0.03mm aluminum foil and reduce aluminum usage by 30%;

2. Composite Structure Optimization: Adopting the “PET/AL/PE” three-layer composite structure allows reducing the aluminum foil layer thickness from 0.03mm to 0.025mm. The 12μm PET layer enhances puncture resistance, and the 30μm PE layer improves heat-sealing performance. Feihe and Junlebao have applied this structure in mass production;

3. 3D Forming Technology: Applying 3D stamping technology to square cans improves the thickness uniformity of aluminum foil at corners by 20%, enabling the lower thickness limit to be reduced from 0.022mm to 0.02mm while maintaining a low cracking rate.

(3) Future Development Directions

1. Sustainable Lightweighting: Developing 0.018mm ultra-thin aluminum foil (combined with graphene coating) ensures barrier performance while reducing aluminum usage by 25%, са 100% recyclability;

2. Intelligent Integration: Embedding RFID smart tags (thickness 50μm) in aluminum foil requires controlling the foil thickness at 0.03-0.035mm to ensure tag adhesion without affecting forming;

3. Antibacterial Function Integration: Loading a silver ion antibacterial layer (thickness 20-30nm) on the aluminum foil surface requires maintaining thickness at 0.028-0.032mm to balance antibacterial performance and mechanical properties, adapting to the microbial control needs of infant milk powder.

6. Закључак

The optimal thickness of aluminum foil for infant milk powder cans requires differentiated design based on can structure:

• Circular Cans: 0.025-0.04мм, with 0.025-0.03mm for small-capacity (180-200г), 0.03-0.035mm for medium-capacity (400-500г), and 0.035-0.04mm for large-capacity (800-1200г);

• Square Cans: 0.022-0.035мм, with 0.022-0.028mm for small-capacity, 0.028-0.032mm for medium-capacity, and 0.032-0.035mm for large-capacity (gradient-thickness design is recommended).

Thickness selection must comprehensively balance barrier performance, mechanical adaptability, compliance requirements, и коштати. Through material modification and process optimization, a balance between “lightweighting and high performance” can be achieved, providing core protection for the quality of infant milk powder.